Dosing and mixing arrangement for use in exhaust aftertreatment

ABSTRACT

A dosing and mixing arrangement is disclosed herein. The arrangement includes a mixing tube having a constant diameter along its length. At least a first portion of the mixing tube includes a plurality of apertures. The arrangement also includes a swirl structure for causing exhaust flow to swirl outside of the first portion of the mixing tube in one direction along a flow path that extends at least 270 degrees around a central axis of the mixing tube. The arrangement is configured such that the exhaust enters an interior of the mixing tube through the apertures as the exhaust swirls along the flow path. The exhaust entering the interior of the mixing tube through the apertures has a tangential component that causes the exhaust to swirl around the central axis within the interior of the mixing tube. The arrangement also includes a doser for dispensing a reactant into the interior of the mixing tube.

CROSS-REFERENCE TO RELATED APPLICATION

The present application claims priority to U.S. Provisional PatentApplication Ser. No. 61/357,418 entitled DOSING AND MIXING ARRANGEMENTFOR USE IN EXHAUST AFTERTREATMENT and filed on Jun. 22, 2010, thedisclosure of which is hereby incorporated by reference in its entirety.

BACKGROUND

Vehicles equipped with internal combustion engines (e.g., dieselengines) typically include exhaust systems that have aftertreatmentcomponents such as selective catalytic reduction (SCR) catalyst devices,lean NOx catalyst devices, or lean NOx trap devices to reduce the amountof undesirable gases, such as nitrogen oxides (NOx) in the exhaust. Inorder for these types of aftertreatment devices to work properly, adoser injects reactants, such as urea, ammonia, or hydrocarbons, intothe exhaust gas. As the exhaust gas and reactants flow through theaftertreatment device, the exhaust gas and reactants convert theundesirable gases, such as NOx, into more acceptable gases, such asnitrogen and oxygen. However, the efficiency of the aftertreatmentsystem depends upon how evenly the reactants are mixed with the exhaustgases. Therefore, there is a need for a flow device that provides auniform mixture of exhaust gases and reactants.

SCR exhaust treatment devices focus on the reduction of nitrogen oxides.In SCR systems, a reductant (e.g., aqueous urea solution) is dosed intothe exhaust stream. The reductant reacts with nitrogen oxides whilepassing through an SCR substrate to reduce the nitrogen oxides tonitrogen and water. When aqueous urea is used as a reductant, theaqueous urea is converted to ammonia which in turn reacts with thenitrogen oxides to covert the nitrogen oxides to nitrogen and water.Dosing, mixing and evaporation of aqueous urea solution can bechallenging because the urea and by-products from the reaction of ureato ammonia can form deposits on the surfaces of the aftertreatmentdevices. Such deposits can accumulate over time and partially block orotherwise disturb effective exhaust flow through the aftertreatmentdevice.

SUMMARY

An aspect of the present disclosure relates to a dosing and mixing unitfor use in exhaust aftertreatment. The dosing and mixing unit includes amixing tube having a generally constant diameter along the length of themixing tube. The mixing tube includes a first portion having a pluralityof apertures (e.g., perforations) and a second portion having a solidwall without any apertures. The mixing tube includes a first endportioned adjacent the first portion of the mixing tube and a second endpositioned adjacent the second portion of the mixing tube. The first endof the mixing tube is closed to exhaust flow and a doser is mounted atthe first end of the mixing tube. The second end of the mixing tube isopen and functions as an outlet for the mixing tube. The dosing andmixing unit also includes a swirling structure for swirling exhaustgenerally circumferentially (i.e., tangentially) around an exterior ofthe first portion of the mixing tube. The swirling exhaust enters thefirst portion of the mixing tube through the apertures of the mixingtube. The exhaust entering the mixing tube through the apertures has atangential flow component that causes the flow to swirl within themixing tube about a central axis of the mixing tube. The swirlingexhaust then flows from the first portion of the mixing tube to thesecond portion of the mixing tube and exits the mixing tube through thesecond end of the mixing tube. The doser injects reactant into theinterior of the mixing tube and the swirling motion of the exhaustwithin the mixing tube assists in uniformly mixing the reactant into theexhaust while the exhaust is within the mixing tube.

Another aspect of the present disclosure relates to a dosing and mixingunit for use in exhaust aftertreatment. The dosing and mixing unitincludes a mixing tube having a plurality of apertures. The dosing andmixing unit also includes a swirl housing partially surrounding themixing tube. The dosing and mixing unit further includes an inlet pipeattached to a side of the swirl housing and extending out from the sideof the swirl housing in an angled tangential direction in relation to acentral axis of the mixing tube. The dosing and mixing unit alsoincludes a swirl structure for causing exhaust flow to swirl along aflow path around the central axis of the mixing tube. In addition, thedosing and mixing unit includes a doser for dispensing a reactant intothe interior of the mixing tube.

In certain embodiments, the swirling structure can include differenttypes of structures for causing the exhaust to swirl about the mixingtube. In one embodiment, the swirling structure can include an outerhousing that at least partially encloses the mixing tube and thatdirects exhaust flow in a swirling motion about the mixing tube. Inanother embodiment, the swirling structure can include a baffle thatdirects exhaust flow in a swirling motion about the mixing tube.

In certain embodiments, dosing and mixing units in accordance with theprinciples of the present disclosure can be used as part of an SCRexhaust treatment system for reducing nitrogen oxides to nitrogen andwater. In such embodiments, the dosing and mixing units can be used todose and mix reductants such as aqueous urea or ammonia at locationsupstream from SCR substrates. In other embodiments, dosing and mixingunits in accordance with the principles of the present disclosure can beused to mix other types of reactants such as hydrocarbons (e.g., fuelssuch as diesel fuel or syngas) upstream from other types of substratessuch as lean NOx catalyst devices, lean NOx traps, catalytic converterssuch as diesel oxidation catalyst (DOC) substrates and dieselparticulate filter (DPF) substrates.

A variety of additional aspects will be set forth in the descriptionthat follows. These aspects can relate to individual features and tocombinations of features. It is to be understood that both the foregoinggeneral description and the following detailed description are exemplaryand explanatory only and are not restrictive of the broad concepts uponwhich the embodiments disclosed herein are based.

DRAWINGS

FIG. 1 is a front view of a doser and mixing unit having features thatare examples of aspects in accordance with the principles of the presentdisclosure;

FIG. 2 is a top view of the doser and mixing unit of FIG. 1;

FIG. 3 is a cross-sectional view taken along section line 3-3 of FIG. 1;

FIG. 4 is a cross-sectional view taken along section line 4-4 of FIG. 1;

FIG. 5 is a front view of an exemplary doser and mixing unit inaccordance with the principles of the present disclosure;

FIG. 6 is a front view of another exemplary doser and mixing unit inaccordance with the principles of the present disclosure;

FIG. 7 is a front view of still another exemplary doser and mixing unitin accordance with the principles of the present disclosure;

FIG. 8 is a front view of a further exemplary doser and mixing unit inaccordance with the principles of the present disclosure;

FIG. 9 is a front view of yet an exemplary doser and mixing unit inaccordance with the principles of the present disclosure;

FIG. 10 is a top view of the doser and mixing unit of FIG. 9;

FIG. 11 is a front view of an aftertreatment device having features thatare examples of aspects in accordance with the principles of the presentdisclosure;

FIG. 12 is a top view of the aftertreatment device of FIG. 11;

FIG. 13 is a front view of a doser and mixing unit having features thatare examples of aspects in accordance with the principles of the presentdisclosure;

FIG. 14 is a schematic representation of a first exhaust treatmentsystem incorporating a doser and mixing unit in accordance with theprinciples of the present disclosure;

FIG. 15 is a schematic representation of a second exhaust treatmentsystem incorporating a doser and mixing unit in accordance with theprinciples of the present disclosure; and

FIG. 16 is a schematic representation of a third exhaust treatmentsystem incorporating a doser and mixing unit in accordance with theprinciples of the present disclosure;

FIG. 17 a-17 f are top views of a dosing and mixing unit showingdifferent means for creating swirl.

DETAILED DESCRIPTION

Reference will now be made in detail to the exemplary aspects of thepresent disclosure that are illustrated in the accompanying drawings.Wherever possible, the same reference numbers will be used throughoutthe drawings to refer to the same or like structure.

FIGS. 1-8 show a dosing and mixing unit 20 in accordance with theprinciples of the present disclosure. The dosing and mixing unit 20includes an inlet 22 and an outlet 24. The inlet 22 is formed by aninlet pipe 26 that extends to a swirl housing 28. The dosing and mixingunit 20 also includes a mixing tube 30 having a first end 32 positionedwithin the swirl housing 28 and a second end 34 that forms the outlet 24of the dosing and mixing unit 20. The inlet pipe 26 is attached to aside 29 of the swirl housing 28 and extends out from the side 29 of theswirl housing 28 in an angled tangential direction in relation to acentral axis 42 of the mixing tube 30. As is illustrated in FIGS. 1, 6and 7, the inlet pipe 26 can be attached to a top portion of the side 27of swirl housing 28 (see FIG. 1) or a lower portion of the side 27 ofswirl housing 28 (see FIG. 6. The inlet pipe 26 can also have differentangles in relation to the central axis 42 such that the exhaust flowenters the swirl housing 28 in a direction towards a bottom of the swirlhousing 28 (see FIGS. 1 and 6) or towards a top end 27 of swirl housing28 (see FIG. 7). In other embodiments (not shown), the inlet pipe 26 isattached to the top end 27 of swirl housing 28 in an angled tangentialdirection in relation to a central axis 42 of the mixing tube 30. Theangle between the inlet pipe 26 and the central axis 42 is in someembodiment an oblique angle.

The mixing tube 30 has a first portion 36 positioned adjacent to thefirst end 32 of the mixing tube 30 and a second portion 38 positionedadjacent to the second end 34 of the mixing tube 30. The first portion36 has a plurality of apertures 37 (e.g., perforations) and the secondportion 38 has a solid wall without any apertures. The apertures 37 canbe formed as circles, squares, slots or any other shape. The dosing andmixing unit 20 also includes a doser 40 mounted to the top end 27 of theswirl housing 28 adjacent to the first end 32 of the mixing tube 30. Thedoser 40 is adapted for dispensing reactant into an interior region ofthe mixing tube 30.

In use of the dosing and mixing unit 20, exhaust enters the dosing andmixing unit 20 through the inlet 22 and is swirled circumferentially(i.e., tangentially) through a swirl structure about the exterior of thefirst portion 36 of the mixing tube 30 by the swirl housing 28. As theexhaust flow swirls circumferentially around the first portion 36 of themixing tube 30, the exhaust gas enters the interior of the mixing tube30 through the apertures 37. The exhaust flow entering the interior ofthe mixing tube 30 through the apertures 37 has atangential/circumferential flow component that causes the exhaust toswirl within the interior of the mixing tube 30. The doser 40 dispensesreactant into the swirling exhaust within the interior of the mixingtube where the swirling action of the exhaust assists in uniformlymixing the reactant within the exhaust. Swirling flow of the exhaustcontinues from the first portion 36 of the mixing tube 30 to the secondportion 38 of the mixing tube 30 whereby mixing is enhanced as theexhaust moves through the length of the mixing tube 30. After theswirling exhaust has traveled through the mixing tube in a directionextending from the first end 32 to the second end 34 of the mixing tube30, the exhaust exits the dosing and mixing unit 20 through the outlet24. As is seen in FIG. 2, the swirl structure has in some embodiments across-section that gradually decreases along the exhaust flow path.

The mixing tube 30 of the dosing and mixing unit 20 defines the centralaxis 42 and has a length that extends along the central axis 42 from thefirst end 32 to the second end 34 of the mixing tube 30. The mixing tube30 is cylindrical in shape and has in some embodiments (shown in FIGS.1-7) a constant diameter along the entire length of the mixing tube 30.Thus, the first and second portions 36, 38 of the mixing tube 30 haveconstant diameters along their respective lengths. Also, the first andsecond portions 36, 38 of the mixing tube 30 are shown having equaldiameters. In some embodiments (shown in FIG. 8), the first end 32 ofthe mixing tube 30 has a larger diameter than the second end 34. In someembodiments, the first portion 36 of the mixing tube 30 has a diameterthat gradually decreases along its length towards the second portion 38.The first end 32 of the mixing tube 30 is blocked by the top end 27 ofswirl housing 28 so that exhaust flow can not pass through the first end32 of the mixing tube 30. In some embodiments, as is seen in FIGS. 5 and8, the first end 32 of the mixing tube 30 is arranged at a distance fromthe top end 27 of the swirl housing 28, forming a gap 52. The doser 40is positioned at the first end 32 of the mixing tube 30 and is alignedalong the central axis 42. As shown at FIGS. 3 and 4, the swirlingmotion of the exhaust can increase in intensity as the swirling exhaustmoves axially through the first portion 36 of the mixing tube in adirection toward the second portion 38 of the mixing tube 38. Thus, bythe time the exhaust enters the second portion 38 of the mixing tube 30,the exhaust is swirling at an increased rate.

In certain embodiments, the doser 40 can include an injector thatinjects reactant in a spray cone aligned along the central axis 42 ofthe mixing tube 30. The swirling action of the exhaust and theconverging flow passing through the apertures 37 (see FIG. 3) assists innarrowing the spray cone angle thereby inhibiting wetting of theinterior of the mixing tube 30 and minimizing deposit formation withinthe mixing tube and downstream from the mixing tube. The swirling actionis particularly suited for breaking-up, mixing and evaporating aqueousurea in a relatively short time frame/distance.

The swirl housing 28 at least partially encloses the first portion 36 ofthe mixing tube 30 and has an arrangement that directs exhaust flowtangentially relative to the outer surface of the mixing tube 30 suchthat the exhaust swirls circumferentially around the exterior of themixing tube 30. In one embodiment, the exhaust flows in a singledirection (e.g., clockwise relative to the central longitudinal axis asshown at FIG. 2) around at least 75 percent of the outer diameter of themixing tube 30. In other words, the exhaust flow direction turns atleast 270 degrees around the outer diameter of the mixing tube 30. Asthe exhaust flows around the mixing tube 30, portions of the exhaustprogressively enter the interior of the first portion 36 of the mixingtube 30 through the apertures 37. The swirl housing 28 has a curved/bentsurface 44 that curves along and opposes the outer surface of the firstportion 36 of the mixing tube 30. The surface 44 is arranged totransition progressively closer to the outer surface of the firstportion 36 of the mixing tube 30 as the surface extends in thecircumferential direction of exhaust flow. In some embodiments (notshown), the mixing tube 30 is arranged such in the swirl housing 28 thatthe central axis 42 of the mixing tube 30 is not in parallel with alongitudinal axis of the swirl housing 28, i.e. the second portion 28 ofthe mixing tube 30 extends from the swirl housing 28 in an angleddirection.

FIGS. 9 and 10 show a dosing and mixing unit 20 that is configured inthe same manner and includes the same features as described inconjunction with FIGS. 1-8. The unit 20 further comprises indents 62 orsome other kind of profile for causing the exhaust to swirl within theinterior of the mixing tube 30. In some embodiments (not shown), theswirl housing 28 includes indents or other kinds of profiles on theinside of the top end 27 for causing the swirl. In other embodiments,the unit 20 includes a screw or helical shaped device arranged aroundthe mixing tube 30 for causing the exhaust to swirl.

FIGS. 11 and 12 show an aftertreatment device 120 in accordance with theprinciples of the present disclosure. The aftertreatment device 120includes an inlet 122 and an outlet 124. The inlet 122 is formed by aninlet pipe 126 that extends to a substrate housing 128. A substrate 129(e.g., a DPF substrate or DOC substrate) is positioned within thesubstrate housing 128 adjacent to the inlet pipe 126. The aftertreatmentdevice 120 also includes a mixing tube 130 having the same configurationas the mixing tube 30. The mixing tube 130 has a first end 132positioned within the substrate housing 128 and a second end 134 thatforms the outlet 124 of the aftertreatment device 120. The mixing tube130 has a first portion 136 positioned adjacent to the first end 132 ofthe mixing tube 130 and a second portion 138 positioned adjacent to thesecond end 134 of the mixing tube 130. The first portion 136 has aplurality of apertures 137 (e.g., perforations) and the second portion138 has a solid wall without any apertures. The apertures 137 can beformed as circles, squares, slots or any other shape. The aftertreatmentdevice 120 also includes a doser 140 mounted to the housing 128 adjacentto the first end 132 of the mixing tube 130. The doser 140 is adaptedfor dispensing reactant into an interior region of the mixing tube 130.A deflector baffle 150 is positioned between the substrate 129 and thefirst portion 136 of the mixing tube 130. The deflector baffle 150 isconfigured to cause the exhaust to flow circumferentially in onedirection around at least 270 degrees of the exterior of the outerdiameter of the first portion 136 of the mixing tube 30. The baffle 150directs the flow in a tangential direction relative to the outerdiameter of the mixing tube 30. In certain embodiments, the mixing tube130 can be bent so that an out put end of the tube angles away from theinlet 122. In other embodiments, the tube 130 can be straight and theentire tube 130 can be angled at angle θ relative to a central axis ofthe housing 128. In certain embodiments, the angle θ is in the range of60-90 degrees. In other embodiments, the angle θ is less than 90degrees, or less than 80 degrees, or in the range of 60-80 degrees. Inother embodiments, the angle θ is 90 degrees. The angle θ is measuredbetween the outer end of the tube 130 and the main body of the housing128.

In another embodiment, the tube 130 can be offset from the center of thehousing 128 so as to be closer to a first side 131 (e.g., a top side) ofthe housing as compared to a second side 133 (e.g., a bottom side) ofthe housing 128.

In use of the aftertreatment device 120, exhaust enters the device 120through the inlet 122 and passes through the substrate 129 where theexhaust is initially treated (e.g., contaminants removed by filtrationor chemically through a catalyzed reaction at the substrate). After theexhaust passes through the substrate 129, the baffle 150 causes theexhaust to swirl circumferentially (i.e., tangentially) through a swirlstructure about the exterior of the first portion 136 of the mixing tube130. As the exhaust flow swirls circumferentially around the firstportion 136 of the mixing tube 130, the exhaust gas enters the interiorof the mixing tube 130 through the apertures 137. The exhaust flowentering the interior of the mixing tube 130 through the apertures 137has a tangential/circumferential flow component that causes the exhaustto swirl within the interior of the mixing tube 130. The doser 140dispenses reactant into the swirling exhaust within the interior of themixing tube where the swirling action of the exhaust assists inuniformly mixing the reactant within the exhaust. Swirling flow of theexhaust continues from the first portion 136 of the mixing tube 130 tothe second portion 138 of the mixing tube 130 whereby mixing is enhancedas the exhaust moves through the length of the mixing tube 130. Afterthe swirling exhaust has traveled through the mixing tube in a directionextending from the first end 132 to the second end 134 of the mixingtube 130, the exhaust exits the device 120 through the outlet 124. As isseen in FIG. 12, the swirl structure has a cross-section that graduallydecreases along the exhaust flow path.

FIG. 13 shows a doser and mixing unit 220 in accordance with theprinciples of the present disclosure. The unit 220 includes an inlet 222and an outlet 224. The inlet 222 is formed by an inlet pipe 226 thatextends to a swirl housing 128. The unit 220 also includes a mixing tube230 having the same configuration as the mixing tube 30 shown anddescribed in conjunction with FIGS. 1-10. As can be seen in FIG. 13, theinlet pipe 226 is arranged with a radial offset from a central axis ofthe mixing tube 230 such that the incoming exhaust through the inlet 222has a flow direction that is generally in parallel of the direction ofthe outgoing exhaust through outlet 224. The mixing tube 230 has a firstend 232 positioned within the swirl housing 228 and a second end 234that forms the outlet 224 of the unit 220. The mixing tube 230 has afirst portion 236 positioned adjacent to the first end 232 of the mixingtube 230 and a second portion 238 positioned adjacent to the second end234 of the mixing tube 230. The first portion 236 has a plurality ofapertures 237 (e.g., perforations) and the second portion 238 has asolid wall without any apertures. The apertures 237 can be formed ascircles, squares, slots or any other shape. The unit 220 also includes adoser 240 mounted to the housing 228 adjacent to the first end 232 ofthe mixing tube 230. The doser 240 is adapted for dispensing reactantinto an interior region of the mixing tube 230. A deflector baffle 250is positioned within the swirl housing 228 between the inlet pipe 226and the first portion 236 of the mixing tube 230. The deflector baffle250 is configured to cause the exhaust to flow circumferentially in onedirection around at least 270 degrees of the exterior of the outerdiameter of the first portion 236 of the mixing tube 230. The baffle 250directs the flow in a tangential direction relative to the outerdiameter of the mixing tube 230.

As the exhaust flow swirls circumferentially around the first portion236 of the mixing tube 230, the exhaust gas enters the interior of themixing tube 230 through the apertures 237. The exhaust flow entering theinterior of the mixing tube 230 through the apertures 237 has atangential/circumferential flow component that causes the exhaust toswirl within the interior of the mixing tube 230. The doser 240dispenses reactant into the swirling exhaust within the interior of themixing tube where the swirling action of the exhaust assists inuniformly mixing the reactant within the exhaust. Swirling flow of theexhaust continues from the first portion 236 of the mixing tube 230 tothe second portion 238 of the mixing tube 230 whereby mixing is enhancedas the exhaust moves through the length of the mixing tube 230. Afterthe swirling exhaust has traveled through the mixing tube 230 in adirection extending from the first end 232 to the second end 234 of themixing tube 230, the exhaust exits the unit 220 through the outlet 224.

FIG. 14 shows a system 300 including the dosing and mixing unit 20. Thesystem includes an internal combustion engine 302. A pipe 304 carriesexhaust from the engine 302 to the dosing and mixing unit 20 wherereactant (e.g., aqueous urea) is injected into the exhaust stream andmixed with the exhaust stream. A pipe 306 carries the exhaust streamcontaining the reactant to an SCR device 308 where nitrogen oxides arereduced to nitrogen and water. FIG. 15 shows a system 400 that is thesame as the system 300 except a separate aftertreatment substrate (e.g.,a DPF or DOC) is positioned between the engine 300 and the dosing andmixing unit 20. FIG. 16 shows a system 500 that is the same as thesystem 300 except the aftertreatment device 120 has been substituted forthe dosing and mixing unit 20.

A selective catalytic reduction (SCR) catalyst device is typically usedin an exhaust system to remove undesirable gases such as nitrogen oxides(NOx) from the vehicle's emissions. SCR's are capable of converting NOxto nitrogen and oxygen in an oxygen rich environment with the assistanceof reactants such as urea or ammonia, which are injected into theexhaust stream upstream of the SCR through the doser 40. In alternativeembodiments, other aftertreatment devices such as lean NOx catalystdevices or lean NOx traps could be used in place of the SCR catalystdevice, and other reactants (e.g., hydrocarbons) can be dispensed by thedoser.

A lean NOx catalyst device is also capable of converting NOx to nitrogenand oxygen. In contrast to SCR's, lean NOx catalysts use hydrocarbons asreducing agents/reactants for conversion of NOx to nitrogen and oxygen.The hydrocarbon is injected into the exhaust stream upstream of the leanNOx catalyst. At the lean NOx catalyst, the NOx reacts with the injectedhydrocarbons with the assistance of a catalyst to reduce the NOx tonitrogen and oxygen. While the exhaust treatment systems 400 and 500will be described as including an SCR, it will be understood that thescope of the present disclosure is not limited to an SCR as there arevarious catalyst devices that can be used in accordance with theprinciples of the present disclosure.

The lean NOx traps use a material such as barium oxide to absorb NOxduring lean burn operating conditions. During fuel rich operations, theNOx is desorbed and converted to nitrogen and oxygen by reaction withhydrocarbons in the presence of catalysts (precious metals) within thetraps.

FIGS. 17 a-17 f are top views of a dosing and mixing unit 20 asdescribed and shown in conjunction with FIGS. 1-10 and show differentmeans for creating exhaust flow swirl. FIG. 17 a illustrates a swirlstructure that has the same cross-section around the outer diameter ofthe mixing tube 30. In the embodiment shown in FIG. 17 b, the swirlhousing 28 includes a stop wall 63 that forces the exhaust flow to enterthe mixing tube 30. In the embodiment shown in FIG. 17 c, the dosing andmixing unit 20 includes one or more flow guide devices 64 arrangedbetween an outer wall of the mixing tube 30 and an inner wall of theswirl housing 28. The flow guide devices 64 may extend from a bottom ofthe swirl housing 28 or from a top of the swirl housing 28. The flowguide device(s) 64 may also be arranged on the inner wall of the swirlhousing 28 (as shown in FIG. 17 d) or on the outer wall of the mixingtube 30 (not shown). Further, according to some embodiments, the mixingtube 30 may be provided with fins 65 inwardly extending from an innerwall of the mixing tube 30 (see FIG. 17 e). FIG. 17 f illustrates thatswirl structure transits from a circular cross-section into an oval orelliptical cross-section along the flow path.

Various modifications and alterations of this disclosure will becomeapparent to those skilled in the art without departing from the scopeand spirit of this disclosure, and it should be understood that thescope of this disclosure is not to be unduly limited to the illustrativeembodiments set forth herein.

1. A dosing and mixing arrangement comprising: a mixing tube having aconstant diameter along its length, at least a first portion of themixing tube including a plurality of apertures; a swirl structure forcausing exhaust flow to swirl outside of the first portion of the mixingtube in one rotational direction along a flow path that extends at least270 degrees around a central axis of the mixing tube, wherein theexhaust enters an interior of the mixing tube through the apertures asthe exhaust swirls along the flow path, and wherein the exhaust enteringthe interior of the mixing tube through the apertures has a tangentialcomponent that causes the exhaust to swirl around the central axiswithin the interior of the mixing tube; and a doser for dispensing areactant into the interior of the mixing tube.
 2. The dosing and mixingarrangement of claim 1, wherein the reactant includes aqueous urea. 3.The dosing and mixing arrangement of claim 1, wherein the swirlstructure includes a swirl housing at least partially surrounding thefirst portion of the mixing tube.
 4. The dosing and mixing arrangementof claim 1, wherein the mixing tube includes a second portion that doesnot have any apertures.
 5. The dosing and mixing arrangement of claim 4,wherein the mixing tube has a first end positioned adjacent the firstportion and a second end positioned adjacent the second portion, andwherein the second end forms an outlet of the mixing tube.
 6. The dosingand mixing arrangement of claim 5, wherein the first end of the mixingtube is closed to exhaust flow and wherein the doser is mounted at thefirst end of the mixing tube.
 7. The dosing and mixing arrangement ofclaim 1, wherein the swirl structure includes a baffle within a housing.8. The dosing and mixing arrangement of claim 1, wherein the firstportion of the mixing tube is positioned within a substrate housingcontaining an aftertreatment substrate positioned upstream from themixing tube, and wherein the swirl structure includes a bafflepositioned between the aftertreatment substrate and the mixing tube. 9.The dosing and mixing arrangement of claim 8, wherein the aftertreatmentsubstrate is selected from the group consisting of a diesel particulatefilter and a catalytic converter.
 10. The dosing and mixing arrangementof claim 1, further comprising an SCR substrate positioned downstreamfrom the mixing tube.
 11. The dosing and mixing arrangement of claim 1,wherein the swirl structure has a cross-section that gradually decreasesalong the flow path.
 12. A dosing and mixing arrangement comprising: amixing tube having a first portion and a second portion, wherein atleast the first portion of the mixing tube including a plurality ofapertures; a swirl housing at least partially surrounding the firstportion of the mixing tube; an inlet pipe being attached to a side ofthe swirl housing and extending out from the side of the swirl housingin an angled tangential direction in relation to a central axis of themixing tube, wherein exhaust enters the swirl housing through the inletpipe; a swirl structure for causing exhaust flow to swirl outside of thefirst portion of the mixing tube in one rotational direction along aflow path around the central axis of the mixing tube, wherein theexhaust enters an interior of the mixing tube through the apertures asthe exhaust swirls along the flow path, and wherein the exhaust enteringthe interior of the mixing tube through the apertures has a tangentialcomponent that causes the exhaust to swirl around the central axiswithin the interior of the mixing tube; and a doser for dispensing areactant into the interior of the mixing tube.
 13. The dosing and mixingarrangement of claim 12, wherein the mixing tube has a constant diameteralong its length.
 14. The dosing and mixing arrangement of claim 12,wherein the mixing tube has a first end positioned adjacent the firstportion and a second end positioned adjacent the second portion, whereina diameter of the first end is larger than a diameter of the second end,and wherein the second end forms an outlet of the mixing tube.
 15. Thedosing and mixing arrangement of claim 12, wherein the mixing tube has afirst end positioned adjacent the first portion and a second endpositioned adjacent the second portion, wherein the first end of themixing tube is closed to exhaust flow, and wherein the doser is mountedat the first end of the mixing tube.
 16. The dosing and mixingarrangement of claim 12, wherein the mixing tube has a first endpositioned adjacent the first portion and a second end positionedadjacent the second portion, wherein a gap is formed between the firstend of the mixing tube and a top end of the swirl housing and whereinthe doser is mounted at the top end of the swirl housing.
 17. The dosingand mixing arrangement of claim 12, wherein the flow path extends atleast 270 degrees around the central axis of the mixing tube.
 18. Thedosing and mixing arrangement of claim 12, wherein the second portion ofthe mixing tube does not have any apertures.
 19. The dosing and mixingarrangement of claim 12, wherein the reactant includes aqueous urea. 20.The dosing and mixing arrangement of claim 12, wherein the swirlstructure contains at least one baffle.
 21. The dosing and mixingarrangement of claim 12, wherein the angle between the inlet pipe andthe central axis is an oblique angle.
 22. A dosing and mixingarrangement comprising: an inlet and an outlet; a main housing bodybetween the inlet and the outlet; a mixing tube having a first portionwithin the main housing body and a second portion projecting outwardlyfrom the main housing body, the first portion defining a plurality ofapertures, the second portion forming the outlet; a swirl structure forswirling exhaust around the first portion of the tube; a doser thatdispenses reactant into the mixing tube; and an exhaust aftertreatmentsubstrate positioned within the main housing body at a location betweenthe inlet and the first portion of the mixing tube.
 23. The dosing andmixing arrangement of claim 22, wherein the exhaust aftertreatmentdevise is selected from the group consisting of a particulate filter anda diesel oxidation catalyst substrate, and wherein a selective catalyticreduction substrate is downstream from the outlet.